David Kirkpatrick

December 23, 2009

Dyeing graphene

I’ve done plenty of blogging on graphene, the world’s thinnest material at a single atom of carbon, and I’ve even posted an actual image of graphene. Now scientists at Northwestern University have found a way to actually dye the material — well, technically the method is more a reverse dyeing — but the result is a great reduction in cost when imaging graphene for certain applications.

From the link:

The useful tool is the dye fluorescein, and Jiaxing Huang, assistant professor of materials science and engineering at the McCormick School of Engineering and Applied Science, and his research group have used the dye to create a new imaging technique to view graphene, a one-atom thick sheet that scientists believe could be used to produce low-cost carbon-based transparent and flexible electronics.

Their results were recently published in the Journal of the American Chemical Society.

Being the world’s thinnest materials, graphene and its derivatives such as graphene oxide are quite challenging to see. Current imaging methods for graphene materials typically involve expensive and time-consuming techniques. For example,  (AFM), which scans materials with a tiny tip, is frequently used to obtain images of graphene materials. But it is a slow process that can only look at small areas on smooth surfaces.  (SEM), which scans a surface with high-energy electrons, only works if the material is placed in vacuum. Some  methods are available, but they require the use of special substrates, too.

Update: Here’s a press release on this exact topic. Find the full text of the release (plus images) below the fold. (more…)

November 17, 2009

Incredible nanotech image — graphene

Filed under: et.al., Science, Technology — Tags: , , , , — David Kirkpatrick @ 10:02 pm

I’ve done lots of blogging on the nanomaterial graphene, and here’s an incredible image of the atom-thick sheet of carbon:

A graphene sheet stretched across a gap in a semiconductor chip. Image: Kirill Bolotkin

And here’s a link to the PhysOrg article accompanying the image.

From the link:

Not only is this the thinnest material possible, but it also is 10 times stronger than steel and it conducts electricity better than any other known material at room temperature. These and graphene’s other exotic properties have attracted the interest of physicists, who want to study them, and nanotechnologists, who want to exploit them to make novel electrical and mechanical devices.

“There are two features that make graphene exceptional,” says Kirill Bolotin, who has just joined the Vanderbilt Department of Physics and Astronomy as an assistant professor. “First, its molecular structure is so resistant to defects that researchers have had to hand-make them to study what effects they have. Second, the electrons that carry  travel much faster and generally behave as if they have far less mass than they do in ordinary metals or superconductors.”

October 12, 2009

The latest on graphene

Filed under: Science, Technology — Tags: , , , , , — David Kirkpatrick @ 5:17 pm

Via KurzweilAI.net:

Growing geodesic carbon nanodomes

KurzweilAI.net, Oct. 12, 2009

Graphene sheets of carbon growing on a surface of iridium grow by first forming tiny carbon domes, researchers in Italy, the UK and USA have discovered, pointing the way to possible methods for assembling components of graphene-based computer circuits, replacing silicon and metal.

The study suggests that graphene grows in the form of tiny islands built of concentric rings of carbon atoms. The islands are strongly bonded to the iridium surface at their perimeters, but are not bonded to the iridium at their centers, which causes them to bulge upward in the middle to form minuscule geodesic domes. By adjusting the conditions as the carbon is deposited on the iridium, the researchers could vary the size of the carbon domes from a few nanometers to hundreds of nanometers across.

More info: October 12 issue of Physics

September 2, 2009

Magnetic graphene

Graphene news from Virginia Commonwealth University:

Researchers design new graphene-based, nano-material with magnetic properties

A possible pathway to simply synthesize ferromagnetic graphene

Ferromagnetic Graphone Sheet. Puru Jena/VCU.

An international team of researchers has designed a new graphite-based, magnetic nano-material that acts as a semiconductor and could help material scientists create the next generation of electronic devices like microchips.

The team of researchers from Virginia Commonwealth University; Peking University in Beijing, China; the Chinese Academy of Science in Shanghai, China; and Tohoku University in Sedai, Japan; used theoretical computer modeling to design the new material they called graphone, which is derived from an existing material known as graphene.

Graphene, created by scientists five years ago, is 200 times stronger than steel, its electrons are highly mobile and it has unique optical and transport properties. Some experts believe that graphene may be more versatile than carbon nanotubes, and the ability to make graphene magnetic adds to its potential for novel applications in spintronics. Spintronics is a process using electron spin to synthesize new devices for memory and data processing.

Although graphene’s properties can be significantly modified by introducing defects and by saturating with hydrogen, it has been very difficult for scientists to manipulate the structure to make it magnetic.

“The new material we are predicting – graphone – makes graphene magnetic simply by controlling the amount of hydrogen coverage – basically, how much hydrogen is put on graphene. It avoids previous difficulties associated with the synthesis of magnetic graphene,” said Puru Jena, Ph.D., distinguished professor in the VCU Department of Physics.

“There are many possibilities for engineering new functional materials simply by changing their composition and structure. Our findings may guide researchers in the future to discover this material in the laboratory and to explore its potential technological applications,” said Jena.

“One of the important impacts of this research is that semi-hydrogenation provides us a very unique way to tailor magnetism. The resulting ferromagnetic graphone sheet will have unprecedented possibilities for the applications of graphene-based materials,” said Qiang Sun, Ph.D., research associate professor with the VCU team.

The study appeared online Aug. 31 in the journal Nano Letters, a publication of the American Chemical Society. The work was supported by a grant from the National Natural Science Foundation of China, The National Science Foundation and by the U.S. Department of Energy. Read the article abstract here.

The first author of this paper is Jian Zhou, a Ph.D. student at Peking University. The other authors include Qian Wang, Ph.D., a research associate professor at VCU; Xiaoshuan Chen, Ph.D., a professor at the Shanghai Institute of Technical Physics; and Yoshiyuki Kawazoe, Ph.D.,  a professor at Tohoku University.

About VCU and the VCU Medical Center:


Virginia Commonwealth University is the largest university in Virginia with national and international rankings in sponsored research. Located on two downtown campuses in Richmond, VCU enrolls 32,000 students in 205 certificate and degree programs in the arts, sciences and humanities. Sixty-five of the programs are unique in Virginia, many of them crossing the disciplines of VCU’s 15 schools and one college. MCV Hospitals and the health sciences schools of Virginia Commonwealth University compose the VCU Medical Center, one of the nation’s leading academic medical centers. For more, see www.vcu.edu.

August 6, 2009

Practical graphene

The previous post was a bit of skylarking on practical solar power, this post is right here on the ground about a current practical application for graphene. I have a feeling I’ve have the opportunity to do many more posts along these lines about the highly touted nanomaterial.

From the first link:

A startup company in Jessup, MD, hopes later this year to bring to market one of the first products based on the nanomaterial graphene. Vorbeck Materials is making conductive inks based on graphene that can be used to print RFID antennas and electrical contacts for flexible displays. The company, which is banking on the low cost of the graphene inks, has an agreement with the German chemical giant BASF and last month received $5.1 million in financing from private-investment firm Stoneham Partners.

Since it was first created in the lab in 2004, graphene has been hailed as a wonder material: the two-dimensional sheets of carbon atoms are the strongest material ever tested, and graphene’s electrical properties make it a potential replacement for silicon in faster computer chips. Synthesizing pristine graphene of the quality needed to make transistors, though, remains a painstaking process that, as yet, can’t be done on an industrial scale, though researchers are working on this problem.

Vorbeck Materials is making what company scientific advisor Ilhan Aksay calls “defective” graphene in large quantities. Though the electrical properties of the graphene aren’t good enough to support transistors, it’s still strong and conductive.

Vorbeck Materials licensed their method for making “crumpled” graphene from Aksay, a professor of chemical engineering at Princeton University. Vorbeck Materials says the inks made with this crumpled graphene are conductive and cheap enough to compete with silver and carbon inks currently used in displays and RFID-tag antennas. (Another startup working on defective graphene, Graphene Energy of Austin, TX, is using a similar form of the material to make electrodes for ultracapacitors.)

Crumpled graphene: Conductive inks made by startup company Vorbeck Materials contain crumpled graphene. This atomic-force microscope image is colorized to show the topography of a piece of graphene of the type used in the inks; red areas are higher and blue are lower. Credit: Ilhan Aksay and Hannes Schniepp

Crumpled graphene: Conductive inks made by startup company Vorbeck Materials contain crumpled graphene. This atomic-force microscope image is colorized to show the topography of a piece of graphene of the type used in the inks; red areas are higher and blue are lower. Credit: Ilhan Aksay and Hannes Schniepp

July 9, 2009

Testing graphene for potential applications

Graphene is proving to be one of the most, if not the most, exciting nanotech discovery of the last few years. The material has a lot of promise in terms of applications in medicine, electronics and who know what else.

Here’s some measurement and testing on putting the nanomaterial to actual use in the market.

The release:

Material world: graphene’s versatility promises new applications

July 09, 2009

Since its discovery just a few years ago, graphene has climbed to the top of the heap of new super-materials poised to transform the electronics and nanotechnology landscape. As N.J. Tao, a researcher at the Biodesign Institute of Arizona State University explains, this two-dimensional honeycomb structure of carbon atoms is exceptionally strong and versatile. Its unusual properties make it ideal for applications that are pushing the existing limits of microchips, chemical sensing instruments, biosensors, ultracapacitance devices, flexible displays and other innovations.

In the latest issue of Nature Nanotechnology Letters, Tao describes the first direct measurement of a fundamental property of graphene, known as quantum capacitance, using an electrochemical gate method. A better understanding of this crucial variable should prove invaluable to other investigators participating in what amounts to a gold rush of graphene research.

Although theoretical work on single atomic layer graphene-like structures has been going on for decades, the discovery of real graphene came as a shock.  “When they found it was a stable material at room temperature,” Tao says,  “everyone was surprised.” As it happens, minute traces of graphene are shed whenever a pencil line is drawn, though producing a 2-D sheet of the material has proven trickier.  Graphene is remarkable in terms of thinness and resiliency. A one-atom thick graphene sheet sufficient in size to cover a football field, would weigh less than a gram. It is also the strongest material in nature—roughly 200 times the strength of steel. Most of the excitement however, has to do with the unusual electronic properties of the material.

Graphene displays outstanding electron transport, permitting electricity to flow rapidly and more or less unimpeded through the material. In fact, electrons have been shown to behave as massless particles similar to photons, zipping across a graphene layer without scattering. This property is critical for many device applications and has prompted speculation that graphene could eventually supplant silicon as the substance of choice for computer chips, offering the prospect of ultrafast computers operating at terahertz speeds, rocketing past current gigahertz chip technology. Yet, despite encouraging progress, a thorough understanding of graphene’s electronic properties has remained elusive. Tao stresses that quantum capacitance measurements are an essential part of this understanding.

Capacitance is a material’s ability to store energy. In classical physics, capacitance is limited by the repulsion of like electrical charges, for example, electrons. The more charge you put into a device, the more energy you have to expend to contain it, in order to overcome charge repulsion. However, another kind of capacitance exists, and dominates overall capacitance in a two-dimensional material like graphene. This quantum capacitance is the result of the Pauli exclusion principle, which states that two fermions—a class of common particles including protons, neutrons and electrons—cannot occupy the same location at the same time. Once a quantum state is filled, subsequent fermions are forced to occupy successively higher energy states. As Tao explains, “it’s just like in a building, where people are forced to go to the second floor once the first level is occupied.”

In the current study, two electrodes were attached to graphene, and a voltage applied across the material’s two-dimensional surface by means of a third, gate electrode. Plots of voltage vs. capacitance can be seen in fig1. In Tao’s experiments, graphene’s ability to store charge according to the laws of quantum capacitance, were subjected to detailed measurement. The results show that graphene’s capacitance is very small. Further, the quantum capacitance of graphene did not precisely duplicate theoretical predictions for the behavior of ideal graphene. This is due to the fact that charged impurities occur in experimental samples of graphene, which alter the behavior relative to what is expected according to theory.

Tao stresses the importance of these charged impurities and what they may mean for the development of graphene devices. Such impurities were already known to affect electron mobility in graphene, though their effect on quantum capacitance has only now been revealed. Low capacitance is particularly desirable for chemical sensing devices and biosensors as it produces a lower signal-to-noise ratio, providing for extremely fine-tuned resolution of chemical or biological agents. Improvements to graphene will allow its electrical behavior to more closely approximate theory. This can be accomplished by adding counter ions to balance the charges resulting from impurities, thereby further lowering capacitance.  

The sensitivity of graphene’s single atomic layer geometry and low capacitance promise a significant boost for biosensor applications. Such applications are a central topic of interest for Tao, who directs the Biodesign Institute’s Center for Bioelectronics and Biosensors. As Tao explains, any biological substance that interacts with graphene’s single atom surface layer can be detected, causing a huge change in the properties of the electrons.

One possible biosensor application under consideration would involve functionalizing graphene’s surface with antibodies, in order to precisely study their interaction with specific antigens. Such graphene-based biosensors could detect individual binding events, given a suitable sample.  For other applications, adding impurities to graphene could raise overall interfacial capacitance. Ultracapacitors made of graphene composites would be capable of storing much larger amounts of renewable energy from solar, wind or wave energy than current technologies permit.

Because of graphene’s planar geometry, it may be more compatible with conventional electronic devices than other materials, including the much-vaunted carbon nanotubes. “You can imagine an atomic sheet, cut into different shapes to create different device properties,” Tao says.

Since the discovery of graphene, the hunt has been on for similar two-dimensional crystal lattices, though so far, graphene remains a precious oddity.

 Advanced Online Publication: http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2009.177.html

 -Written by Richard Harth
Science Writer
Biodesign Institute

June 12, 2009

Graphene and tunable semiconductors

A double dose of graphene news for tonight.

The release:

Tunable semiconductors possible with hot new material called graphene

Tunable bandgap means tunable transistors, LEDs and lasers

Berkeley — Today’s transistors and light emitting diodes (LED) are based on silicon and gallium arsenide semiconductors, which have fixed electronic and optical properties.

Now, University of California, Berkeley, researchers have shown that a form of carbon called graphene has an electronic structure that can be controlled by an electrical field, an effect that can be exploited to make tunable electronic and photonic devices.

While such properties were predicted for a double layer of graphene, this is the first demonstration that bilayer graphene exhibits an electric field-induced, broadly tunable bandgap, according to principal author Feng Wang, UC Berkeley assistant professor of physics.

The bandgap of a material is the energy difference between electrons residing in the two most important states of a material – valence band states and conduction band states – and it determines the electrical and optical properties of the material.

“The real breakthrough in materials science is that for the first time you can use an electric field to close the bandgap and open the bandgap. No other material can do this, only bilayer graphene,” Wang said.

Because tuning the bandgap of bilayer graphene can turn it from a metal into a semiconductor, a single millimeter-square sheet of bilayer graphene could potentially hold millions of differently tuned electronic devices that can be reconfigured at will, he said.

Wang, post-doctoral fellow Yuanbo Zhang, graduate student Tsung-Ta Tang and their UC Berkeley and Lawrence Berkeley National Laboratory (LBNL) colleagues report their success in the June 11 issue of Nature.

“The fundamental difference between a metal and a semiconductor is this bandgap, which allows us to create semiconducting devices,” said coauthor Michael Crommie, UC Berkeley professor of physics. “The ability to simply put a material between two electrodes, apply an electric field and change the bandgap is a huge deal and a major advance in condensed matter physics, because it means that in a device configuration we can change the bandgap on the fly by sending an electrical signal to the material.”

Graphene is a sheet of carbon atoms, each atom chemically bonded to its three neighbors to produce a hexagonal array that looks a lot like chicken wire. Since it was first isolated from graphite, the material in pencil lead, in 2004, it has been a hot topic of research, in part because solid state theory predicts unusual electronic properties, including a high electron mobility more than 10 times that of silicon.

However, the property that makes it a good conductor – its zero bandgap – also means that it’s always on.

“To make any electronic device, like a transistor, you need to be able to turn it on or off,” Zhang said. “But in graphene, though you have high electron mobility and you can modulate the conductance, you can’t turn it off to make an effective transistor.”

Semiconductors, for example, can be turned off because of a finite bandgap between the valence and conduction electron bands.

While a single layer of graphene has a zero bandgap, two layers of graphene together theoretically should have a variable bandgap controlled by an electrical field, Wang said. Previous experiments on bilayer graphene, however, have failed to demonstrate the predicted bandgap structure, possibly because of impurities. Researchers obtain graphene with a very low-tech method: They take graphite, like that in pencil lead, smear it over a surface, cover with Scotch tape and rip it off. The tape shears the graphite, which is just billions of layers of graphene, to produce single- as well as multi-layered graphene.

Wang, Zhang, Tang and their colleagues decided to construct bilayer graphene with two voltage gates instead of one. When the gate electrodes were attached to the top and bottom of the bilayer and electrical connections (a source and drain) made at the edges of the bilayer sheets, the researchers were able to open up and tune a bandgap merely by varying the gating voltages.

The team also showed that it can change another critical property of graphene, its Fermi energy, that is, the maximum energy of occupied electron states, which controls the electron density in the material.

“With top and bottom gates on bilayer graphene, you can independently control the two most important parameters in a semiconductor: You can change the electronic structure to vary the bandgap continuously, and independently control electron doping by varying the Fermi level,” Wang said.

Because of charge impurities and defects in current devices, the graphene’s electronic properties do not reflect the intrinsic graphene properties. Instead, the researchers took advantage of the optical properties of bandgap materials: If you shine light of just the right color on the material, valence electrons will absorb the light and jump over the bandgap.

In the case of graphene, the maximum bandgap the researchers could produce was 250 milli-electron volts (meV). (In comparison, the semiconductors germanium and silicon have about 740 and 1,200 meV bandgaps, respectively.) Putting the bilayer graphene in a high intensity infrared beam produced by LBNL’s Advanced Light Source (ALS), the researchers saw absorption at the predicted bandgap energies, confirming its tunability.

Because the zero to 250 meV bandgap range allows graphene to be tuned continuously from a metal to a semiconductor, the researchers foresee turning a single sheet of bilayer graphene into a dynamic integrated electronic device with millions of gates deposited on the top and bottom.

“All you need is just a bunch of gates at all positions, and you can change any location to be either a metal or a semiconductor, that is, either a lead to conduct electrons or a transistor,” Zhang said. “So basically, you don’t fabricate any circuit to begin with, and then by applying gate voltages, you can achieve any circuit you want. This gives you extreme flexibility.”

“That would be the dream in the future,” Wang said.

Depending on the lithography technique used, the size of each gate could be much smaller than one micron – a millionth of a meter – allowing millions of separate electronic devices on a millimeter-square piece of bilayer graphene.

Wang and Zhang also foresee optical applications, because the zero-250 meV bandgap means graphene LEDs would emit frequencies anywhere in the far- to mid-infrared range. Ultimately, it could even be used for lasing materials generating light at frequencies from the terahertz to the infrared.

“It is very difficult to find materials that generate light in the infrared, not to mention a tunable light source,” Wang said.

Crommie noted, too, that solid state physicists will have a field day studying the unusual properties of bilayer graphene. For one thing, electrons in monolayer graphene appear to behave as if they have no mass and move like particles of light – photons. In tunable bilayer graphene, the electrons suddenly act as if they have masses that vary with the bandgap.

“This is not just a technological advance, it also opens the door to some really new and potentially interesting physics,” Crommie said.

 

###

 

Wang, Zhang, Tang and their colleagues continue to explore graphene’s electronic properties and possible electronic devices.

Their coauthors are Crommie, Alex Zettl and Y. Ron Shen, UC Berkeley professors of physics; physics post-doctoral fellow Caglar Girit; and Zhao Hao and Michael C. Martin of LBNL’s ALS Division. Zhang is a Miller Post-doctoral Fellow at UC Berkeley.

The work was supported by the U.S. Department of Energy.

Assembly with graphene

Interesting research on the properties of one of the more exciting nanotech materials out there.

The release:

Penn materials scientist finds plumber’s wonderland on graphene

IMAGE: This is an electron micrograph showing the formation of interconnected carbon nanostructures on a graphene substrate, which may be harnessed to make future electronic devices.

Click here for more information. 

PHILADELPHIA –- Engineers from the University of Pennsylvania, Sandia National Laboratories and Rice University have demonstrated the formation of interconnected carbon nanostructures on graphene substrate in a simple assembly process that involves heating few-layer graphene sheets to sublimation using electric current that may eventually lead to a new paradigm for building integrated carbon-based devices.

Curvy nanostructures such as carbon nanotubes and fullerenes have extraordinary properties but are extremely challenging to pick up, handle and assemble into devices after synthesis. Penn materials scientist Ju Li and Sandia scientist Jianyu Huang have come up with a novel idea to construct curvy nanostructures directly integrated on graphene, taking advantage of the fact that graphene, an atomically thin two-dimensional sheet, bends easily after open edges have been cut on it, which can then fuse with other open edges permanently, like a plumber connecting metal fittings.

The “knife” and “welding torch” used in the experiments, which were performed inside an electron microscope, was electrical current from a Nanofactory scanning probe, generating up to 2000°C of heat. Upon applying the electrical current to few-layer graphene, they observed the in situ creation of many interconnected, curved carbon nanostructures, such as “fractional nanotube”-like graphene bi-layer edges, or BLEs; BLE rings on graphene equivalent to “anti quantum-dots”; and nanotube-BLE assembly connecting multiple layers of graphene.

Remarkably, researchers observed that more than 99 percent of the graphene edges formed during sublimation were curved BLEs rather than flat monolayer edges, indicating that BLEs are the stable edges in graphene, in agreement with predictions based on symmetry considerations and energetic calculations. Theory also predicts these BLEs, or “fractional nanotubes,” possess novel properties of their own and may find applications in devices.

The study is published in the current issue of the journal Proceedings of the National Academy of Sciences. Short movies of the fabrication of these nanostructures can be viewed at www.youtube.com/user/MaterialsTheory.

Li and Huang observed the creation of these interconnected carbon nanostructures using the heat of electric current and a high-resolution transmission electron microscope. The current, once passed through the graphene layers, improved the crystalline quality and surface cleanness of the graphene as well, both important for device fabrication.

The sublimation of few-layer graphene, such as a 10-layer stack, is advantageous over the sublimation of monolayers. In few-layer graphene, layers spontaneously fuse together forming nanostructures on top of one or two electrically conductive, extended, graphene sheets.

During heating, both the flat graphene sheets and the self-wrapping nanostructures that form, like bilayer edges and nanotubes, have unique electronic properties important for device applications. The biggest obstacle for engineers has been wrestling control of the structure and assembly of these nanostructures to best exploit the properties of carbon. The discoveries of self-assembled novel carbon nanostructures may circumvent the hurdle and lead to new approach of graphene-based electronic devices.

Researchers induced the sublimation of multilayer graphene by Joule-heating, making it thermodynamically favorable for the carbon atoms at the edge of the material to escape into the gas phase, leaving freshly exposed edges on the solid graphene. The remaining graphene edges curl and often welded together to form BLEs. Researchers attribute this behavior to nature’s driving force to reduce capillary energy, dangling bonds on the open edges of monolayer graphene, at the cost of increased bending energy.

“This study demonstrates it is possible to make and integrate curved nanostructures directly on flat graphene, which is extended and electrically conducting,” said Li, associate professor in the Department of Materials Science and Engineering in Penn’s School of Engineering and Applied Science. “Furthermore, it demonstrates that multiple graphene sheets can be intentionally interconnected. And the quality of the plumbing is exceptionally high, better than anything people have used for electrical contacts with carbon nanotubes so far. We are currently investigating the fundamental properties of graphene bi-layer edges, BLE rings and nanotube-BLE junctions.”

 

###

 

The study was performed by Li and Liang Qi of Penn, Jian Yu Huang and Ping Lu of the Center for Integrated Nanotechnologies at Sandia and Feng Ding and Boris I. Yakobson of the Department of Mechanical Engineering and Materials Science at Rice.

It was supported by the National Science Foundation, the Air Force Office of Scientific Research, the Honda Research Institute, the Department of Energy and the Office of Naval Research.

June 5, 2009

Graphene beats copper in IC connections

It’s been a while since I’ve had the chance to blog about graphene, but here is the latest on the carbon nanomaterial.  (Be sure to hit the second link for images.)

The release:

Graphene May Have Advantages Over Copper for Future IC Interconnects

New Material May Replace Traditional Metal at Nanoscale Widths

Atlanta (June 4, 2009) —The unique properties of thin layers of graphite—known as graphene—make the material attractive for a wide range of potential electronic devices. Researchers have now experimentally demonstrated the potential for another graphene application: replacing copper for interconnects in future generations of integrated circuits.

In a paper published in the June 2009 issue of the IEEE journal Electron Device Letters, researchers at the Georgia Institute of Technology report detailed analysis of resistivity in graphene nanoribbon interconnects as narrow as 18 nanometers.

The results suggest that graphene could out-perform copper for use as on-chip interconnects—tiny wires that are used to connect transistors and other devices on integrated circuits. Use of graphene for these interconnects could help extend the long run of performance improvements for silicon-based integrated circuit technology.

“As you make copper interconnects narrower and narrower, the resistivity increases as the true nanoscale properties of the material become apparent,” said Raghunath Murali, a research engineer in Georgia Tech’s Microelectronics Research Center and the School of Electrical and Computer Engineering. “Our experimental demonstration of graphene nanowire interconnects on the scale of 20 nanometers shows that their performance is comparable to even the most optimistic projections for copper interconnects at that scale. Under real-world conditions, our graphene interconnects probably already out-perform copper at this size scale.”

Beyond resistivity improvement, graphene interconnects would offer higher electron mobility, better thermal conductivity, higher mechanical strength and reduced capacitance coupling between adjacent wires.

“Resistivity is normally independent of the dimension—a property inherent to the material,” Murali noted. “But as you get into the nanometer-scale domain, the grain sizes of the copper become important and conductance is affected by scattering at the grain boundaries and at the side walls. These add up to increased resistivity, which nearly doubles as the interconnect sizes shrink to 30 nanometers.”

The research was supported by the Interconnect Focus Center, which is one of the Semiconductor Research Corporation/DARPA Focus Centers, and the Nanoelectronics Research Initiative through the INDEX Center.

Murali and collaborators Kevin Brenner, Yinxiao Yang, Thomas Beck and James Meindl studied the electrical properties of graphene layers that had been taken from a block of pure graphite. They believe the attractive properties will ultimately also be measured in graphene fabricated using other techniques, such as growth on silicon carbide, which now produces graphene of lower quality but has the potential for achieving higher quality.

Because graphene can be patterned using conventional microelectronics processes, the transition from copper could be made without integrating a new manufacturing technique into circuit fabrication.

“We are optimistic about being able to use graphene in manufactured systems because researchers can already grow layers of it in the lab,” Murali noted. “There will be challenges in integrating graphene with silicon, but those will be overcome. Except for using a different material, everything we would need to produce graphene interconnects is already well known and established.”

Experimentally, the researchers began with flakes of multi-layered graphene removed from a graphite block and placed onto an oxidized silicon substrate. They used electron beam lithography to construct four electrode contacts on the graphene, then used lithography to fabricate devices consisting of parallel nanoribbons of widths ranging between 18 and 52 nanometers. The three-dimensional resistivity of the nanoribbons on 18 different devices was then measured using standard analytical techniques at room temperature.

The best of the graphene nanoribbons showed conductivity equal to that predicted for copper interconnects of the same size. Because the comparisons were between non-optimized graphene and optimistic estimates for copper, they suggest that performance of the new material will ultimately surpass that of the traditional interconnect material, Murali said.

“Even graphene samples of moderate quality show excellent properties,” he explained. “We are not using very high levels of optimization or especially clean processes. With our straightforward processing, we are getting graphene interconnects that are essentially comparable to copper. If we do this more optimally, the performance should surpass copper.”

Though one of graphene’s key properties is reported to be ballistic transport—meaning electrons can flow through it without resistance—the material’s actual conductance is limited by factors that include scattering from impurities, line-edge roughness and from substrate phonons—vibrations in the substrate lattice.

Use of graphene interconnects could help facilitate continuing increases in integrated circuit performance once features sizes drop to approximately 20 nanometers, which could happen in the next five years, Murali said. At that scale, the increased resistance of copper interconnects could offset performance increases, meaning that without other improvements, higher density wouldn’t produce faster integrated circuits.

“This is not a roadblock to achieving scaling from one generation to the next, but it is a roadblock to achieving increased performance,” he said. “Dimensional scaling could continue, but because we would be giving up so much in terms of resistivity, we wouldn’t get a performance advantage from that. That’s the problem we hope to solve by switching to a different materials system for interconnects.”

March 20, 2009

Graphene to speed up microchips

Filed under: Science, Technology — Tags: , , , — David Kirkpatrick @ 2:36 pm

I’ve done plenty of blogging about graphene, and it’s about time for a new breakthrough. Graphene looks to be one of the nanomaterials that is readily translating into real-world applications.

Via KurzweilAI.net:

Graphene could lead to faster chips
PhysOrg.com, Mar. 19, 2009

New research findings at MIT could lead to microchips using graphene technology that allows them to operate at much higher speeds (in the 500 to 1,000 gigahertz range) than is possible with today’s standard silicon chips, leading to cell phones and other communications systems that can transmit data much faster.

 
Read Original Article>>

January 21, 2009

Latest on graphene — various substrate growth

Graphene is one of nanotech’s serious breakthroughs and here’s the latest on the single-atom thick carbon material.

The release:

Light-Speed Nanotech: Controlling the Nature of Graphene

Researchers at Rensselaer have developed a new method for controlling the conductive nature of graphene. Pictured is a rendering of two sheets of graphene, each with the thickness of just a single carbon atom, resting on top of a silicon dioxide substrate.

Researchers “tune” graphene’s properties by growing it on different surfaces

Researchers at Rensselaer Polytechnic Institute have discovered a new method for controlling the nature of graphene, bringing academia and industry potentially one step closer to realizing the mass production of graphene-based nanoelectronics.

Graphene, a one-atom-thick sheet of carbon, was discovered in 2004 and is considered a potential heir to copper and silicon as the fundamental building blocks of nanoelectronics. 

With help from an underlying substrate, researchers for the first time have demonstrated the ability to control the nature of graphene. Saroj Nayak, an associate professor in Rensselaer’s Department of Physics, Applied Physics, and Astronomy, along with Philip Shemella, a postdoctoral research associate in the same department, have determined that the chemistry of the surface on which graphene is deposited plays a key role in shaping the material’s conductive properties. The results are based on large-scale quantum mechanical simulations.

Results show that when deposited on a surface treated with oxygen, graphene exhibits semiconductor properties. When deposited on a material treated with hydrogen, however, graphene exhibits metallic properties.

“Depending on the chemistry of the surface, we can control the nature of the graphene to be metallic or semiconductor,” Nayak said. “Essentially, we are ‘tuning’ the electrical properties of material to suit our needs.” 

Conventionally, whenever a batch of graphene nanostructures is produced, some of the graphene is metallic, while the rest is semiconductor. It would be nearly impossible to separate the two on a large scale, Nayak said, yet realizing new graphene devices would require that they be comprised solely of metallic or semiconductor graphene. The new method for “tuning” the nature of graphene is a key step to making this possible, he said. 

Graphene’s excellent conductive properties make it attractive to researchers. Even at room temperature, electrons pass effortlessly, near the speed of light and with little resistance. This means a graphene interconnect would likely stay much cooler than a copper interconnect of the same size. Cooler is better, as heat produced by interconnects can have negative effects on both a computer chip’s speed and performance.

Results of the study were published this week in the paper “Electronic structure and band-gap modulation of graphene via substrate surface chemistry” in Applied Physics Letters, and are featured on the cover of the journal’s January 19 issue. 

Large-scale quantum simulations for the study were run on Rensselaer’s supercomputing system, the Computational Center for Nanotechnology Innovations (CCNI). 

Researchers received funding for the project from the New York State Interconnect Focus Center at Rensselaer.

Published January 20, 2009

December 17, 2008

Graphene improving transistors

Haven’t blogged about the nanotech material graphene in a while. Here’s some exciting news from Technology Review.

From the link:

A pair of research groups, working independently, report making graphene-based transistors that work at the highest frequencies reported to date. The new transistors are a promising first step toward ultrahigh radio-frequency (RF) transistors, which could be useful for wireless communications, remote sensing, radar systems, and weapons imaging systems.

The reports come from researchers at the IBM T. J. Watson Research Center in Yorktown Heights, NY, and at the HRL Laboratories in Malibu, CA. The IBM transistors work at frequencies up to 26 gigahertz. Both the IBM and HRL work was funded by the U.S. military’s Defense Advanced Research Projects Agency (DARPA). Kostya Novoselov, a physicist and graphene researcher at the University of Manchester, in the U.K., says that the results are “a really big step forward to demonstrating that high-frequency graphene transistors should work.”

Graphene, a flat sheet of carbon atoms, is a promising material for RF transistors. Typical RF transistors are made from silicon or more expensive semiconductors like indium phosphide. In graphene, for the same voltage, electrons zip around 10 times faster than in indium phosphide, or 100 times faster than in silicon.

Graphene transistors will also consume less power and could turn out to be cheaper than those made from silicon or indium phosphide. Yu-Ming Lin, who led the work at IBM, says that silicon technology is extremely mature, but graphene could “achieve device performance that may never be obtained with conventional semiconductors.”

Jeong-Sun Moon, HRL Laboratories

Speedy carbon devices: Researchers at HRL Laboratories create high-frequency transistors on top of two-inch-wide graphene pieces by patterning metal electrodes and depositing insulating aluminum oxide on top of the graphene. Credit: Jeong-Sun Moon, HRL Laboratories

November 18, 2008

Latest graphene news — practicality

From KurzweilAI.net — It’s been awhile since I’ve blogged on graphene. For a time there news was coming out hard and fast about the nanomaterial. The latest news comes out of UCLA on a relataively simple method of creating large (well, large in the nanoscale sense) pieces of graphene.

Making Graphene More Practical
Technology Review, Nov. 18, 2008

Researchers at the University of California, Los Angeles, have found a simple way to make large pieces (tens of micrometers wide) of the carbonmaterial graphene that can be deposited on sheets on silicon wafers to make prototype field-effect transistors.

Electrons flow through graphene sheets tens of times faster than they flow in silicon, so graphene could lead to electronic devices that are smaller, faster, and less power-hungry than those made of silicon. Thin and transparent, graphene is also a promising replacement for the indium tin oxide electrodes and the silicon thin-film transistors used in flat-panel displays.

 
Read Original Article>>

September 25, 2008

The latest news on graphene

Filed under: Science, Technology — Tags: , , — David Kirkpatrick @ 4:58 pm

I’ve done a lot of graphene blogging and here’s the latest on the atom-thick carbon nanomaterial.

The release:

New Graphene-Based Material Clarifies Graphite Oxide Chemistry

September 25, 2008

AUSTIN, Texas — A new “graphene-based” material that helps solve the structure of graphite oxide and could lead to other potential discoveries of the one-atom thick substance called graphene, which has applications in nanoelectronics, energy storage and production, and transportation such as airplanes and cars, has been created by researchers at The University of Texas at Austin.

 

To get an idea of the nanomaterial graphene, imagine a lightweight material having the strongest chemical bond in nature and, thus, exceptional mechanical properties. In addition it conducts heat better than any other material and has charge carriers moving through it at a significant fraction of the speed of light. Just an atom thick, graphene consists of a “chickenwire” (or honeycomb) bonding arrangement of carbon atoms—also known as a single layer of graphite.

Mechanical Engineering Professor Rod Ruoff and his co-authors have, for the first time, prepared carbon-13 labeled graphite. They did this by first making graphite that had every “normal” carbon atom having the isotope carbon-12, which is magnetically inactive, replaced with carbon-13, which is magnetically active. They then converted that to carbon-13 labeled graphite oxide and used solid-state nuclear magnetic resonance to discern the detailed chemical structure of graphite oxide.

The work by Ruoff’s team will appear in the Sept. 26 issue of the journal Science.

“As a result of our work published in Science, it will now be possible for scientists and engineers to create different types of graphene (by using carbon-13 labeled graphene as the starting material and doing further chemistry to it) and to study such graphene-based materials with solid-state nuclear magnetic resonance to obtain their detailed chemical structure,” Ruoff says. “This includes situations such as where the graphene is mixed with a polymer and chemically bonded at critical locations to make remarkable polymer matrix composites; or embedded in glass or ceramic materials; or used in nanoelectronic components; or mixed with an electrolyte to provide superior supercapacitor or battery performance. If we don’t know the chemistry in detail, we won’t be able to optimize properties.”

Graphene-based materials are a focus area of research at the university because they are expected to have applications for ultra-strong yet lightweight materials that could be used in automobiles and airplanes to improve fuel efficiency, the blades of wind turbines for improved generation of electrical power, as critical components in nanoelectronics that could have blazing speeds but very low power consumption, for electrical energy storage in batteries and supercapacitors to enable renewable energy production at a large scale and in transparent conductive films that will be used in solar cells and image display technology. In almost every application, sensitive chemical interactions with surrounding materials will play a central role in understanding and optimizing performance.

Ruoff and his team proved they had made such an isotopically labeled material from measurements by co-author Frank Stadermann of Washington University in St Louis. Stadermann used a special mass spectrometer typically used for measuring the isotope abundances of various elements that are in micrometeorites that have landed on Earth. Then, 100 percent carbon-13 labeled graphite was converted to 100 percent carbon-13 labeled graphite oxide, also a layered material but with some oxygen atoms attached to the graphene by chemical bonds.

Co-authors Yoshitaka Ishii and Medhat Shaibat of the University of Illinois-Chicago then used solid state nuclear magnetic resonance to help reveal the detailed chemical bonding network in graphite oxide. Ruoff says even though graphite oxide was first synthesized more than150 years ago the distribution of oxygen atoms has been debated even quite recently.

“The ability to control the isotopic labeling between carbon-12 and carbon-13 will lead to many other sorts of studies,” says Ruoff, who holds the Cockrell Family Regents Chair in Engineering #7.

He collaborates on other graphene projects with other university scientists and engineers such as Allan MacDonald (Departments of Physics and Astronomy), Sanjay Banerjee, Emanuel Tutuc and Bhagawan Sahu (Department of Electrical and Computer Engineering) and Gyeong Hwang (Department of Chemical Engineering), and some of these collaborations include industrial partners such as Texas Instruments, IBM and others.

Co-authors on the Science article include: Weiwei Cai, Richard Piner, Sungjin Park, Dongxing Yang, Aruna Velamakanni, Meryl Stoller and Jinho An (all of the Ruoff research group at The University of Texas at Austin); Sung Jin An, formerly of Pohang University of Science and Technology (POSTECH-Korea) and a visiting graduate student in the Ruoff group during the study; Dongmin Chen (Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences); Stadermann; and Ishii and Shaibat of the University of Illinois-Chicago.

A high-resolution photo of Ruoff is available. Learn more about Ruoff’s work.

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  • September 18, 2008

    Graphene to double capacity of ultracapacitors

    Filed under: Science, Technology — Tags: , , , , — David Kirkpatrick @ 10:47 am

    From KurzweilAI.net — Looks like our old (well, new but well covered at this point) friend, graphene, will double the capacity of electric storage ultracapacitors.

    New Carbon Material Shows Promise Of Storing Large Quantities Of Renewable Electrical Energy
    Science News, Sep. 17, 2008

    University of Texas at Austin researchers have developed graphene-based ultracapacitor cells that could double the capacity of ultracapacitors, used to store electrical charge.

     
    Read Original Article>>

    September 8, 2008

    Is graphene going to be the new semiconductor?

    Filed under: Science, Technology — Tags: , , , , , — David Kirkpatrick @ 10:22 pm

    Here’sa report from PhysOrg on graphene replacing semiconductors in the next generation computer chip:

    When one looks at the structure of graphite, stacked layers of pure carbon are apparent. However, it wasn’t until 2004 that a process sophisticated enough to “slice” off one of the layers was discovered. This single layer is called graphene. Graphene is basically a sheet of bonded carbon atoms, with the thickness of only one atom. If one could look down at graphene from the top, one would observe that the sheet bears a strong resemblance to honeycomb, with its hexagons fitted snugly together.

    “Graphene behaves almost like semiconductor but without a energy gap,” Kim explains. This is why it would do well as a material for computer chips. “When you apply an electric field perpendicular to graphene, the number of electrons – the carrier density – can be tuned.”

    “One of the main themes is how fast the charge can move in graphene,” Kim continues. “Higher mobility means electron conducts faster in the system. It has always been speculated that the mobility of graphene can be quite high. But it has not been shown as high as some of the highest semiconductors in the past.”

    August 11, 2008

    Graphene is amazing

    Filed under: Science, Technology — Tags: , , , — David Kirkpatrick @ 8:17 pm

    The nanomaterial has now been used to create the world’s thinnest balloon, and it’s impermeable to any gas molecule. Crazy.

    From the link:

    Graphene, a single layer of graphite, is the upper limit: A chemically stable and electrically conducting membrane just one atom thick. The researchers wanted to answer whether such an atomic membrane would be impermeable to gas molecules and easily incorporated into other devices.

    Their data showed that graphene membranes were impermeable to even the smallest gas molecules. These results show that single atomic sheets can be integrated with microfabricated structures to create a new class of atomic scale membrane-based devices. We envision many applications for these graphene sealed microchambers, says McEuen. These range from hyper-sensitive pressure, light and chemical sensors to filters able to produce ultrapure solutions.

    Jonathan Alden
    Scientists have developed the world’s thinnest balloon that is impermeable to even the smallest gas molecules. Above is a multi-layer graphene membrane that could be used in various applications, including filters and sensors. Image: Jonathan Alden

     Update — I left this out of the original post. If you want more information about graphene, I’ve blogged about the nanomaterial before here, here, here and in the last item here.

     

    April 18, 2008

    Single atom thick graphene transistors

    Filed under: Science, Technology — Tags: , , , , , — David Kirkpatrick @ 2:48 pm

    From KurzweilAI.net:

    Atom-thick material runs rings around silicon
    NewScientist.com news service, April 17, 2008

    University of Manchester researchers have used graphene to make some of the smallest transistors ever, at one atom thick and ten atoms wide.


    credit: MU Mesoscopic Physics Group

    They found that cutting small quantum dots of graphene gave the material switchable conductivity. Dots just a few nanometers across trap electrons due to quantum effects, and applying a magnetic field to the smallest dots lets current flow again, making a switchable transistor. The smallest dots that worked as transistors contained as few as five carbon rings–around 10 atoms or 1 nm wide.

    Previous graphene transistors were significantly bigger–ribbons 10 nm across and many times longer.

     
    Read Original Article>>

    September 3, 2010

    Cool nanotech image — a 2-water molecule thick ice crystal

    Researchers used graphene to trap the room-temperature ice on a mica surface.

    Atomic force micrograph of ~1 micrometer wide × 1.5 micrometers (millionths of a meter) tall area. The ice crystals (lightest blue) are 0.37 nanometers (billionths of a meter) high, which is the height of a 2-water molecule thick ice crystal. A one-atom thick sheet of graphene is used to conformally coat and trap water that has adsorbed onto a mica surface, permitting it to be imaged and characterized by atomic force microscopy. Detailed analysis of such images reveals that this (first layer) of water is ice, even at room temperature. At high humidity levels, a second layer of water will coat the first layer, also as ice. At very high humidity levels, additional layers of water will coat the surface as droplets. Credit: Heath group/Caltech

    Hit the link for the full story on this image.

    May 28, 2010

    Nanotech and DNA sequencing

    Put the two together and you’ve got a solution for a major problem with the genome sequencing technique called nanopore translocation. And yet another application is found for graphene.

    From the link:

    But how do you measure the electrical properties of a single subunit among many tens or hundreds of thousands?

    One of the most promising ideas is to make a tiny hole through a thin sheet of material and measure the amount of current that passes from one side of the sheet to another.

    Next, pull a strand of DNA through this hole and measure the current again. Any difference must be caused by the nucleotide base that happens to blocking the hole at that moment.

    So measuring the way the current changes as you pull the strand through the hole gives you a direct reading of the sequence of nucleotide bases in the strand.

    Simple really. Except for one small problem. Even the thinnest films of semiconducting materials used for this process, such as silicon nitride, are between 10 and 100 times thicker than the distance between two nucleotide bases on a strand of DNA.

    So when a strand of DNA passes through the hole, it’s not a single nucleotide base that blocks it but as many as 100. That makes it hard to determine the sequence from any change in the current.

    Today, Grégory Schneider and buddies at the Kavli Institute of Nanoscience in The Netherlands present a solution to this problem. Instead of a conventional material, this team has used graphene, which is relatively easy to produce in sheets just a single atom thick.

    Graphene is like a sheet of chicken wire made of carbon atoms. These guys have drilled holes of various diameters through just such a sheet using an electron beam to smash carbon atoms out of the structure.

    March 7, 2010

    Carbon nanotubes open new area of energy research

    Nanotechnology is revolutionizing how we see and deal with electricity, everything from storage to wiring. Now a team at MIT has discovered carbon nanotubes produce electricity in an entirely new way, opening a brand new area in energy research.

    From the final link:

    A team of scientists at MIT have discovered a previously unknown phenomenon that can cause powerful waves of energy to shoot through minuscule wires known as carbon nanotubes. The discovery could lead to a new way of producing electricity, the researchers say.

    The phenomenon, described as thermopower waves, “opens up a new area of energy research, which is rare,” says Michael Strano, MIT’s Charles and Hilda Roddey Associate Professor of Chemical Engineering, who was the senior author of a paper describing the new findings that appeared in  on March 7. The lead author was Wonjoon Choi, a doctoral student in mechanical engineering.

    Like a collection of flotsam propelled along the surface by waves traveling across the ocean, it turns out that a thermal wave — a moving pulse of heat — traveling along a microscopic wire can drive electrons along, creating an electrical current.

    The key ingredient in the recipe is carbon nanotubes — submicroscopic hollow tubes made of a chicken-wire-like lattice of carbon atoms. These tubes, just a few billionths of a meter () in diameter, are part of a family of novel carbon molecules, including buckyballs and graphene sheets, that have been the subject of intensive worldwide research over the last two decades.

    February 5, 2010

    Graphane the superconductor

    Back-to-back single-atom layer sheets of carbon nanotech posts today. Graphene and now graphane. (Hit this link for all my graphene blogging and this one for graphane blogging.)

    I’m just going to let this physics arXiv blog post do the explaining on this news:

    New calculations reveal that p-doped graphane should superconduct at 90K, making possible an entirely new generation of devices cooled by liquid nitrogen.

    There’s a problem with high temperature superconductors. It’s now more than two decades since the discovery that certain copper oxides can superconduct at temperatures above 30 K.

    And:

    The implications of all this are astounding. First up is the possibility of useful superconducting devices cooled only by liquid nitrogen. At last!

    But there’s another, more exotic implication: by creating transistor-like gates out of graphane doped in different ways, it should be possible to create devices in which the superconductivity can be switched on and off. That’ll make possible an entirely new class of switch.

    Before all of that, however, somebody has to make p-doped graphane. That will be hard. Graphane itself was made for the first time only last year at the University of Manchester. It should be entertaining to follow the race to make and test a p-doped version.

    November 21, 2009

    Carbon nanotube supercapacitors

    Flawed carbon nanotubes may lead to supercapacitors.

    From the link:

    Most people would like to be able to charge their cell phones and other personal electronics quickly and not too often. A recent discovery made by UC San Diego engineers could lead to carbon nanotube-based supercapacitors that could do just this.

    In recent research, published in , Prabhakar Bandaru, a professor in the UCSD Department of Mechanical and Aerospace Engineering, along with graduate student Mark Hoefer, have found that artificially introduced defects in nanotubes can aid the development of supercapacitors.

    “While batteries have large , they take a long time to charge; while electrostatic capacitors can charge quickly but typically have limited capacity. However, supercapacitors/electrochemical capacitors incorporate the advantages of both,” Bandaru said.

    Of course I mostly ran this post just to add to the excuse for running this awesome image of a carbon nanotube. Earlier this week I featured an incredible image of graphene. We’re getting some just simply amazing looks into the atomic world right now. And it’ll only get better.

    Carbon nanotubes could serve as supercapacitor electrodes with enhanced charge and energy storage capacity (inset: a magnified view of a single carbon nanotube).

    Credit: UC San Diego

    November 3, 2009

    Breakthrough in large-scale nanotube processing

    Via KurzweilAI.net — These manufacturing breakthroughs aren’t as exciting and sexy as a groundbreaking medical application or replacing copper wiring with carbon nanotubes or graphene, but they are key to turning nanotechnology into a viable industry.

    Breakthrough In Industrial-scale Nanotube Processing
    ScienceDaily, Nov. 3, 2009

    Rice University scientists have unveiled a method for high-throughput industrial-scale processing of carbon-nanotube fibers, using chlorosulfonic acid as a solvent.

    The process that could lead to revolutionary advances in materials science, power distribution and nanoelectronics.

     

    Read Original Article>>

    September 10, 2009

    Graphite, data storage and semiconductors

    Interesting release from Rice involving graphite and nanotechnology, but not the usual carbon nanotubes, graphene or graphane.

    The release:

    Graphitic memory techniques advance at Rice

    Researchers simplify fabrication of nano storage, chip-design tools

    Advances by the Rice University lab of James Tour have brought graphite’s potential as a mass data storage medium a step closer to reality and created the potential for reprogrammable gate arrays that could bring about a revolution in integrated circuit logic design.

    In a paper published in the online journal ACS Nano, Tour and postdoctoral associate Alexander Sinitskii show how they’ve used industry-standard lithographic techniques to deposit 10-nanometer stripes of amorphous graphite, the carbon-based, semiconducting material commonly found in pencils, onto silicon. This facilitates the creation of potentially very dense, very stable nonvolatile memory for all kinds of digital devices.

    With backing from a major manufacturer of memory chips, Tour and his team have pushed the technology forward in several ways since a paper that appeared last November first described two-terminal graphitic memory. While noting advances in other molecular computing techniques that involve nanotubes or quantum dots, he said none of those have yet proved practical in terms of fabrication.

    Not so with this simple-to-deposit graphite. “We’re using chemical vapor deposition and lithography — techniques the industry understands,” said Tour, Rice’s Chao Professor of Chemistry and a professor of mechanical engineering and materials science and of computer science. “That makes this a good alternative to our previous carbon-coated nanocable devices, which perform well but are very difficult to manufacture.”

    Graphite makes a good, reliable memory “bit” for reasons that aren’t yet fully understood. The lab found that running a current through a 10-atom-thick layer of graphite creates a complete break in the circuit — literally, a gap in the strip a couple of nanometers wide. Another jolt repairs the break. The process appears to be indefinitely repeatable, which provides addressable ones and zeroes, just like today’s flash memory devices but at a much denser scale.

    Graphite’s other advantages were detailed in Tour’s earlier work: the ability to operate with as little as three volts, an astoundingly high on/off ratio (the amount of juice a circuit holds when it’s on, as opposed to off) and the need for only two terminals instead of three, which eliminates a lot of circuitry. It’s also impervious to a wide temperature range and radiation; this makes it suitable for deployment in space and for military uses where exposure to temperature extremes and radiation is a concern.

    Tour’s graphite-forming technique is well-suited for other applications in the semiconductor industry. One result of the previous paper is a partnership between the Tour group and NuPGA (for “new programmable gate arrays”), a California company formed around the research to create a new breed of reprogrammable gate arrays that could make the design of all kinds of computer chips easier and cheaper.

    The Tour lab and NuPGA, led by industry veteran Zvi Or-Bach (founder of eASIC and Chip Express), have applied for a patent based on vertical arrays of graphite embedded in “vias,” the holes in integrated circuits connecting the different layers of circuitry. When current is applied to a graphite-filled via, the graphite alternately splits and repairs itself (a process also described in the latest paper), just like it does in strip form. Essentially, it becomes an “antifuse,” the basic element of one type of field programmable gate array (FPGA), best described as a blank computer chip that uses software to rewire the hardware.

    Currently, antifuse FPGAs can be programmed once. But this graphite approach could allow for the creation of FPGAs that can be reprogrammed at will. Or-Bach said graphite-based FPGAs would start out as blanks, with the graphite elements split. Programmers could “heal” the antifuses at will by applying a voltage, and split them with an even higher voltage.

    Such a device would be mighty handy to computer-chip designers, who now spend many millions to create the photolithography mask sets used in chip fabrication. If the design fails, it’s back to square one.

    “As a result of that, people are only hesitantly investing in new chip designs,” said Tour. “They stick with the old chip designs and make modifications. FPGAs are chips that have no specific ability, but you use software to program them by interconnecting the circuitry in different ways.”  That way, he said, fabricators don’t need expensive mask sets to try new designs.

    “The No. 1 problem in the industry, and one that gives an opportunity for a company like ours, is that the cost of masks keeps moving up as people push semiconductors into future generators,” said Or-Bach. “Over the last 10 years, the cost of a mask set has multiplied almost 10 times.

    “If we can really make something that will be an order of magnitude better, the markets will be happy to make use of it. That’s our challenge, and I believe the technology makes it possible for us to do that.”

    The ACS Nano paper appears here: http://pubs.acs.org/doi/pdf/10.1021/nn9006225

    Read more about Tour’s research of graphitic memory here: 
    http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=11817

    To download images, go here: http://www.rice.edu/nationalmedia/images/graphitestripes.jpg
    http://www.rice.edu/nationalmedia/images/graphitestripes2.jpg
    http://www.rice.edu/nationalmedia/images/vias.jpg

    July 31, 2009

    Introducing graphane

    Filed under: Science — Tags: , , , , , — David Kirkpatrick @ 3:58 pm

    I’ve done plenty of blogging on the nanomaterial graphene, now here’s an introduction to graphane, its insulating offshoot. Just like with graphene, there’s high hopes for graphane applications.

    The release:

    From graphene to graphane, now the possibilities are endless

    Ever since graphene was discovered in 2004, this one-atom thick, super strong, carbon-based electrical conductor has been billed as a “wonder material” that some physicists think could one day replace silicon in computer chips.

    But graphene, which consists of carbon atoms arranged in a honeycomb lattice, has a major drawback when it comes to applications in electronics – it conducts electricity almost too well, making it hard to create graphene-based transistors that are suitable for integrated circuits.

    In August’s Physics World, Kostya Novoselov – a condensed-matter physicist from the Manchester University group that discovered graphene — explains how their discovery of graphane, an insulating equivalent of graphene, may prove more versatile still.

    Graphane has the same honeycomb structure as graphene, except that it is “spray-painted” with hydrogen atoms that attach themselves to the carbon. The resulting bonds between the hydrogen and carbon atoms effectively tie down the electrons that make graphene so conducting. Yet graphane retains the thinness, super-strength, flexibility and density of its older chemical cousin.

    One advantage of graphane is that it could actually become easier to make the tiny strips of graphene needed for electronic circuits. Such structures are currently made rather crudely by taking a sheet of the material and effectively burning away everything except the bit you need. But now such strips could be made by simply coating the whole of a graphene sheet – except for the strip itself – with hydrogen. The narrow bit left free of hydrogen is your conducting graphene strip, surrounded by a much bigger graphane area that electrons cannot go down.

    As if this is not enough, the physicists in Manchester have found that by gradually binding hydrogen to graphene they are able to drive the process of transforming a conducting material into an insulating one and watch what happens in between.

    Perhaps most importantly of all, the discovery of graphane opens the flood gates to further chemical modifications of graphene. With metallic graphene at one end and insulating graphane at the other, can we fill in the divide between them with, say, graphene-based semiconductors or by, say, substituting hydrogen for fluorine?

    As Professor Novoselov writes, “Being able to control the resistivity, optical transmittance and a material’s work function would all be important for photonic devices like solar cells and liquid-crystal displays, for example, and altering mechanical properties and surface potential is at the heart of designing composite materials. Chemical modification of graphene – with graphane as its first example – uncovers a whole new dimension of research. The capabilities are practically endless.”

     

    ###

    April 6, 2009

    April 2009 media tips from Oak Ridge National Laboratory

    The latest story ideas coming out of Oak Ridge National Laboratory.

    The release:

    April 2009 Story Tips

    Story ideas from the Department of Energy’s Oak Ridge National Laboratory.

    Sensors—Math to the rescue . . .

    Making sense of the enormous amounts of information delivered by all types of sensors is an incredible challenge, but it’s being met head on with knowledge discovery techniques developed at Oak Ridge National Laboratory. Some of the strategies and approaches are outlined in a recently published book, “Knowledge Discovery from Sensor Data,” (http://books.google.com/books?id=dq7uAA3ssPcC) edited by a team led by Auroop Ganguly of ORNL’s Computational Sciences and Engineering Division. The book is specifically aimed at analyzing dynamic data streams from sensors that are geographically distributed. “We are especially interested in looking for changes – even ones that are very gradual — and anomalies,” Ganguly said. This work helps to validate and assign uncertainties to models developed to understand issues related to climate, transportation and biomass. Co-authors include Olufemi Omitaomu and Ranga Raju Vatsavai of ORNL. This research was originally funded by the Laboratory Directed Research and Development program. 

    Cyber Security—Meeting of minds . . .

    Dozens of the nation’s authorities on cyber security will be participating in the Fifth Cyber Security and Information Intelligence Research Workshop April 13-15 (http://www.ioc.ornl.gov/csiirw). The focus of this event, which is open to the public, is to discuss novel theoretical and empirical research to advance the field. “We aim to challenge, establish and debate a far-reaching agenda that broadly and comprehensively outlines a strategy for cyber security and information intelligence that is founded on sound principles and technologies,” said Frederick Sheldon, general chair and a member of Oak Ridge National Laboratory’s Computational Sciences and Engineering Division, a sponsor of the workshop. Other sponsors are the University of Tennessee and the Federal Business Council. The workshop, hosted by ORNL, is being held in cooperation with the Association for Computing Machinery. 

    Material—Graphene cleanup . . .

    Graphene, a single-layer sheet of graphite, has potential as a remarkable material, particularly for electronics and composite applications. However, working with the material leaves molecular-scale rough edges, which can spoil its properties. Researchers at MIT and the Laboratory for Nanoscience and Nanotechnology Research (LINAN) and Advanced Materials Department in San Luis Potosi, Mexico have been working with graphitic nanoribbons. Separate research performed at the Department of Energy’s Oak Ridge National Laboratory developed theory-based computer simulations with quantum mechanical calculations that explain how a process called Joule heating cleans up graphene as the rough carbon edges vaporize and then reconstruct at higher, voltage-induced temperatures. The collaborative project was recently described in Science magazine. 

    Energy—Tighten up . . .

    An effort to gather environmental data related to the energy efficiency of buildings through weatherization technologies will be conducted in a joint project that includes Oak Ridge National Laboratory’s Building Technologies, Research and Integration Center. ORNL engineer Andre Desjarlais says his group’s research will focus on the study of a building’s air tightness by monitoring unintended air movement – air leakage – between outdoors and indoors. In heating climates, up to 30 percent of the energy used in a building can be attributed to air leakage. The tests will be conducted at Syracuse University, which is also a partner. Other partners are the Air Barrier Association of America and it members, along with the New York State Energy Office. The DOE funding source is the Office of Building Technologies.

    December 19, 2008

    Nanotech transistor from IBM to improve cell phone

    Filed under: Business, Technology — Tags: , , , , , , , — David Kirkpatrick @ 11:11 am

    I’ve done some recent blogging on nanotech transistors (this post is on the very subject of the post you’re reading) and it looks like IBM has something gearing up for market-ready to improve cell phone range and battery life.

    From the second link:

    Researchers at the company are using nanotechnology to build a future generation of wireless transceivers that are much more sensitive than the ones found in phones today. They’ll also be made with a less expensive material, according to IBM. The catch is that the new chips probably won’t make it into consumers’ hands for another five or ten years.

    The scientists, sponsored by DARPA (the U.S. Defense Advanced Research Projects Agency), have built prototype transistors with the new material, called graphene. It is a form of graphite that consists of a single layer of carbon atoms arranged in a honeycomb pattern. Graphene’s structure allows electrons to travel through it very quickly and gives it greater efficiency than existing transceiver chip materials, said Yu-Ming Lin, a research staff member at IBM in Yorktown Heights, New York. The project is part of DARPA’s CERA (Carbon Electronics for radio-frequency applications) program.

    August 11, 2008

    Digital Matter project gets $3M

    From KurzweilAI.net:

    $3 million grant awarded to build ‘digital matter’
    KurzweilAI.net, Aug.10, 2008

    Research in diamond mechanosynthesis (DMS) — building diamond nanostructures atom by atom using scanning probe microscopy — just received a major boost with a $3 million grant from the U.K. Engineering and Physical Sciences Research Council, awarded to Professor Philip Moriarty at the University of Nottingham for a “Digital Matter” project, the Nanofactory Collaboration plans to announce Monday.


    Diamond mechanosynthesis with computer-automated tooltip (artist’s impression)

    The Nottingham work grew out of continuing discussions since 2005 on DMS between Moriarty and Robert A. Freitas Jr., a Senior Research Fellow at the Institute for Molecular Manufacturing (IMM).

    “Diamond mechanosynthesis is the key technology that will let us fabricate atomically precise diamond products, including molecular computers, microbivores, and a host of other molecular machines,” said IMM Senior Fellow Ralph Merkle in an email interview. Merkle co-founded the Nanofactory Collaboration with Freitas in 2001 to pursue molecular manufacturing via DMS.

    “There’s a body of theoretical work that says diamond mechanosynthesis is feasible, including specific computational chemistry analyses of specific reactions and specific reaction pathways. Now we have to make it happen in the lab, and Moriarty’s work is the first step along this path.”

    In April 2008, Freitas and Merkle published the results of a comprehensive three-year project to computationally analyze a complete set of DMS reaction sequences and an associated minimal set of tooltips that could be used to build basic diamond and graphene (e.g., carbon nanotube) structures. These structures include all of the tools themselves, along with the necessary tool recharging reactions.

    Moriarty is interested in testing the viability of positionally controlled atom-by-atom fabrication of diamondoid materials as described in the Freitas-Merkle minimal toolset theory paper. Moriarty’s efforts will be the first time that specific predictions made by sophisticated computational chemistry software in the area of mechanosynthesis will be rigorously tested by experiment.

    His work also directly addresses the requirement for “proof of principle” mechanosynthesis experiments requested in the 2006 National Nanotechnology Initiative (NNI) review, in the 2007 Battelle/Foresight nanotechnology roadmap, and by EPSRC’s Strategic Advisor for Nanotechnology, Richard Jones (Physics, Sheffield University, U.K.).

    Also see:
    Mechanosynthesis toolset is important new step toward the nanofactory

    August 1, 2008

    Nanotech creates better plastic

    Filed under: Science, Technology — Tags: , , , , , — David Kirkpatrick @ 1:19 pm

    From KurzweilAI.net:

    New nanomaterial that makes plastic stiffer, lighter and stronger
    Nanowerk News, July 31, 2008

    Michigan State University researchers have developed a graphene-based nanomaterial, xGnP Exfoliated Graphite NanoPlatelets, that makes plastic stiffer, lighter and stronger and could result in more fuel-efficient airplanes and cars as well as more durable medical and sports equipment.

     
    Read Original Article>>

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